The Troubling Loss of Antocha Crane Flies

By Greg McMillan and Rick Hafele

Antocha is just one genus of the family Tipulidae, a group well known as crane flies. As crane flies go Antocha is rather small, and while most crane fly larvae live in slow moving or stagnant water with silty or muddy substrate (some are also terrestrial), Antocha larvae prefer riffle areas of streams with clean cobble substrate. This little crane fly is found throughout North America, including most if not all of the streams in the Deschutes watershed. Until recently it was one of the insects of the lower Deschutes River that appeared every summer in moderate to large numbers. Whether trout found it of interest could be debated, but its presence was one of those reminders that summer had arrived on the lower Deschutes - but no longer.

Rick Hafele and Greg McMillan first noted the absence of Antocha crane flies in the lower Deschutes River in July of 2013. Until that time these dipterids had been abundant in the lower Deschutes River. By the summer of 2013 other species of aquatic insects had also been observed to be in decline, but Antocha just seemed to have disappeared.

We waited until 2014 to confirm our 2013 observations regarding the missing Antocha before saying anything publicly. We reported our observations here in our blog, and then through the observations of others in our 2014 Lower Deschutes River Macroinvertebrate Hatch Activity Survey Results. Our reports regarding the missing crane flies were initially met with little interest, if not skepticism, by resource management agencies and the Pelton-Round Butte Dam operators, but then confirmed by the R2 Resources Interim Report in the Portland General Electric Aquatic Macroinvertebrate and Periphyton Study. The final report from that study also notes that the disappearance of the crane flies in the lower Deschutes River occurred after the inception of selective water withdrawal at Round Butte Dam.

The final report from the PGE Lower Deschutes Aquatic Macroinvertebrate and Periphyton Study also mentions studies done on the Crooked River and Middle Deschutes (Vinson, 2005; and Vinson and Dinger, 2007; Reports prepared for U.S. Department of the Interior, Bureau of Land Management, National Aquatic Monitoring Center) that showed declines in Antocha populations in those rivers. It is worth noting that those studies were done in the years prior to implementation of surface water withdrawal from Lake Billy Chinook at Round Butte Dam in late 2009.

The PGE study concludes that:

“… Antocha crane flies were widely distributed in pre-SWW samples above and below the project but nearly absent post-SWW from nearly all sites including the Deschutes and Crooked Rivers upstream from the project. Significant numbers were observed post-SWW only in the Metolius River, a unique spring-dominated system with minimal development compared to the Crooked and Deschutes systems. Most likely, this change is a result of a broader environmental pattern as opposed to project-related effect. It is unknown whether this pattern represents normal annual variability or a longer term (sic) trend. However, this observation highlights the value of the upstream study sites in distinguishing project from non-project changes.” (Final Report, Lower Deschutes River Macroinvertebrate and Periphyton Study, R2 Resource Consultants, 2016, page 100.)

That conclusion seems to be hastily arrived at, and appears to us to be biased towards exonerating dam operations as a contributor to the disappearance of Antocha in the lower river. Yes, studies show that Antocha crane flies have nearly disappeared from the Crooked and Deschutes rivers above the project, and that decline happened prior to surface water withdrawal from Round Butte Dam. Even though the loss of Antocha is still evident a decade after it was first reported, the PGE report suggests that this could be due to “annual variability.”

The study’s authors go on to suggest that the only other alternative is that this is due to a “broader environmental pattern.” Yet they state that the Antocha population is intact in the Metolius River.

In another aquatic invertebrate study of Whychus Creek, Antocha was found to be present from 2005-2014 (Mazzacano, Effectiveness Monitoring in Whychus Creek; Benthic Macroinvertebrate Communities in 2005, 2009, and 2011-2014, The Xerces Society for Invertebrate Conservation, page 58).

Whychus Creek is a tributary to the Middle Deschutes River. The confluence of Whychus Creek and the Middle Deschutes River is about three miles above Lake Billy Chinook. A great deal of habitat restoration work has taken place in Whychus Creek in recent years thanks to the work of groups like the Deschutes Land Trust, the Upper Deschutes Watershed Council, Trout Unlimited, and others. The Portland General Electric Pelton Fund, along with other sources, has provided funding for this work.

So in at least two other streams the Antocha populations are intact. It would be interesting to look at other streams in the basin to see what the status of Antocha is. We believe it was very hasty and preemptive to draw the conclusion that this is due to a “broader environmental pattern” when only limited data is available from other streams.

Basin studies show that the Middle Deschutes and Crooked rivers have large anthropogenic influences due to population centers and agricultural runoff. That in turn results in higher levels of nutrients that lead to algae growth. As noted in our 2015 Lower Deschutes River Macroinvertebrate Hatch Activity Survey Results, Antocha crane flies lay eggs in the splash zone of river rocks. Stalked diatom algae, which have become common in the lower Deschutes River since implementation of surface water withdrawal from Lake Billy Chinook, form a barrier to the bare rock Antocha seem to favor for reproduction in the lower Deschutes River. This probably makes egg laying impossible.

From mid-November until late May the water discharged from the Pelton-Round Butte Hydroelectric Project consists of 100% surface water draw from Lake Billy Chinook. Even during summer and fall months, there is a minimum of 35% surface water draw (Pelton Round Butte Project, FERC No. 2030, Water Quality Report, 2015). We know that for much of the year, surface water in the forebay of Round Butte Dam consists primarily of water from the Crooked and Middle Deschutes rivers (Deschutes River Alliance 2015 Water Quality Report and unpublished data from 2016, pending publication in 2017).

Given that Antocha crane flies disappeared from the Crooked and Middle Deschutes rivers prior to the institution of surface water withdrawal, and surface water withdrawal is heavily influenced by the water quality of these rivers, we believe that there is another hypothesis for the massive decline of Antocha in the lower Deschutes River. We propose that the causative agent of Antocha decline in those rivers is now being passed down into the lower Deschutes River as a consequence of surface water withdrawal at Round Butte Dam.

That cause could be any, or a combination, of several possible agents.

The first is the nutrients in surface water withdrawal at Round Butte Dam fueling the stalked diatom proliferation in the lower river, which is denying access to clean rock surfaces necessary for Antocha mating and egg-laying.

The second possible cause is that a pesticide or other agent entering the Crooked and Middle Deschutes Rivers is being transferred downstream in surface water from Lake Billy Chinook.

Antocha crane flies have also been found to be susceptible to parasitic infestations (International Review of Hydrobiology, Vol. 92. Issue 4-5, pg. 545-553, August 2007). This raises a host of issues that could possibly be related to the ecological changes brought by surface water withdrawal from Lake Billy Chinook. A parasite could have been transported to the lower river via surface water withdrawal at Round Butte Dam, or water conditions changed by surface water withdrawal, could now be favoring a parasite that has possibly infected Antocha.

How important is the disappearance of Antocha crane flies? That is hard to tell. However their disappearance from the lower Deschutes River, and the Crooked and Middle Deschutes rivers, should be taken as an indication of an ecological change. Their disappearance warrants deeper investigation and not just casual dismissal of a phenomenon that could be indicative of a larger ecological problem.